Method and apparatus for single pass two-color ink jet point of sale (POS) printing

ABSTRACT

A 2-color ink jet point of sale (POS) printer includes a converter for converting full color printing commands into a commands for printing in two colors, a primary color and an alternate color. A three color image is possible when using the background color of the paper as a color. The printer includes a print carriage which contains only two print cartridges. The printer determines a location of the print cartridge relative to a print location of the image to be printed, and when the print cartridges are both on one side of the print location, the print carriages traverses the paper in one direction, printing first with the primary color and then with the alternate color on the same pass. After the paper is advanced in the printer, the print carriage traverses the paper in the other direction, with the alternate color printing before the primary color.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.09/544,941 filed Apr. 7, 2000 now U.S. Pat. No. 6,206,504 and entitledMETHOD AND APPARATUS FOR TWO-COLOR INK JET POINT OF SALE (POS) PRINTING.

FIELD OF THE INVENTION

The invention pertains to the field of ink jet printers, and inparticular, to a point-of-sale (POS) printer that prints two colorsusing a single pass for each line.

BACKGROUND OF THE INVENTION

There are two ways to define colors, CMY and RGB. CMY stands for Cyan,Magenta, and Yellow. Mixing cyan, magenta, and yellow can be comparedblending paint. When cyan, magenta, and yellow are amalgamated together,the result is black. CMY is sometimes known as CMYK, which stands forCyan, Magenta, Yellow and blacK (so as not to be confused with Blue).These colors are sometimes called process colors, because you use themin four-color printing. If you have a typical full color printer, theinks used consist of these primary colors. The term “primary colors”mean that mixing these colors together can create all colors. Cyan,magenta and yellow are theoretically all one needs, but to save costlycolor inks many printers also have a black cartridge. The CMY colormodel is called a subtractive color model, because the process inkpigments “subtracts” or absorbs certain colors and reflects others.

RGB stands for red, green, and blue. Mixing red, green, and bluetogether can be compared to blending light beams. When the lights off,everything looks black. If all the lights are on, the result is white.The RGB model is used in a television or computer monitor. The coloredspots of a TV screen emit three colors, and the sum of these colorsdetermines the color you see. This is called an additive color model.Each color in the RGB system has a value for the amount of Red, Greenand Blue in each picture element (pixel). In the internal Microsoft®Windows® image descriptions, this value goes from 0 to 255, where 0 forall three colors equals black, and 255 for all three colors equalswhite. This means that one can get more than 16 million different colors(TrueColor) because 256*256*256=16,777,216, but one can only get 256shades of gray.

A full color printer forms the various colors of an image by mixing inksof different colors on the paper. That is, a full color printer uses theCMY or CMYK color system. The amount of each color determines the hue.Typically the paper is white and no ink produces a white dot. Mixingyellow and cyan produces a red dot and mixing cyan, magenta, and yellowin equal amounts produces a black or gray dot.

Hue describes what shade of color a particular color is, such as red,orange, indigo, or green. As in the rainbow, the starting and endingcolor is red. Hue can be described as a color circle with red at 0degrees, yellow at 60 degrees clockwise, continuing with green, cyan,blue, magenta, and red again at 360 degrees. Saturation is a term usedwith how bright the color is.

There are a number of different types of printers commerciallyavailable, but not all types are suited to be POS printers. POS printersare used to print cash register receipts or credit card chargestatements. Full color printing is not required, nor is the ability toprint on different types of paper. POS printers tend to be compact so asnot to clutter up a cashier's work area.

Many types of POS single color printers are commercially available. Dotmatrix printers, thermal printers, and ink jet printers are all usedbecause of their speed and reliability. POS color printers are rare inthe marketplace. POS dot matrix color printers require a multi-coloredribbon, which adds to the complexity and size of the printer. Colorthermal printers are under development, but it is hard to do colorgraphics on a thermal printer. In addition, special paper is required.Color ink jet printers are unsuitable for POS printers because addingthree additional ink jet cartridges for full color (also known as4-color, i.e., three colors plus black) would add width and complexityto the printer.

A two-color printer typically makes one pass with the primary colorfollowed by one pass with the alternate color. This is normally becauseof the time it takes to process and send the printer commands to theprinter. In some cases, especially with technologically older inks, twopasses are required to ensure that one color dries before the secondcolor is printed.

SUMMARY OF THE INVENTION

Briefly stated, a 2-color ink jet point of sale (POS) printer includes aconverter for converting full color printing commands into a commandsfor printing in two colors, a primary color and an alternate color. Athree color image is possible when using the background color of thepaper as a color. The printer includes a print carriage which containsonly two print cartridges. The printer determines a location of theprint cartridge relative to a print location of the image to be printed,and when the print cartridges are both on one side of the printlocation, the print carriages traverses the paper in one direction,printing first with the primary color and then with the alternate coloron the same pass. After the paper is advanced in the printer, the printcarriage traverses the paper in the other direction, with the alternatecolor printing before the primary color.

According to an embodiment of the invention, a method of printing athree color image, wherein the three colors are a primary color, analternate color, and a background color, includes the steps of (a)providing a two-color printer for printing the image on a paper; (b)providing a plurality of printer commands representing data from theimage to be printed, the data being in a form of primary color dot data,alternate color dot data, and no-print dot data; (c) determining alocation of a printer carriage with respect to a print location of theimage being printed on the paper, wherein the printer carriage containsonly two print cartridges, namely, a primary color cartridge and analternate color cartridge corresponding to the primary color and thealternate color, respectively; (d) moving the printer carriage to asecond side of the print location if the printer carriage is on a firstside of the print location, and when the primary color cartridge is overthe print location, one primary color dot is printed on the paper wherecalled for by the primary color dot data; after which, when thealternate color cartridge is over the print location, one alternatecolor dot is printed on the paper when called for by the alternate colordot data; (e) stopping the print carriage from moving from the firstside to the second side once both print cartridges are to the secondside of the print location; (f) moving the printer carriage to the firstside of the print location if the printer carriage is on the second sideof the print location, and when the alternate color cartridge is overthe print location, one alternate color dot is printed on the paperwhere called for by the alternate color dot data; after which, when theprimary color cartridge is over the print location, one primary colordot is printed on the paper when called for by the primary color dotdata; and (g) stopping the print carriage from moving from the secondside to the first side once both print cartridges are to the first sideof the print location.

According to an embodiment of the invention, an apparatus for printing athree color image, wherein the three colors are a primary color, analternate color, and a background color, includes a two-color printerfor printing the image on a paper; means for providing a plurality ofprinter commands representing data from the image to be printed, thedata being in a form of primary color dot data, alternate color dotdata, and no-print dot data; means for determining a location of aprinter carriage with respect to a print location of the image beingprinted on the paper, wherein the printer carriage contains only twoprint cartridges, namely, a primary color cartridge and an alternatecolor cartridge corresponding to the primary color and the alternatecolor, respectively; means for moving the printer carriage to a secondside of the print location if the printer carriage is on a first side ofthe print location, and when the primary color cartridge is over theprint location, one primary color dot is printed on the paper wherecalled for by the primary color dot data; after which, when thealternate color cartridge is over the print location, one alternatecolor dot is printed on the paper when called for by the alternate colordot data; means for stopping the print carriage from moving from thefirst side to the second side once both print cartridges are to thesecond side of the print location; means for moving the printer carriageto the first side of the print location if the printer carriage is onthe second side of the print location, and when the alternate colorcartridge is over the print location, one alternate color dot is printedon the paper where called for by the alternate color dot data; afterwhich, when the primary color cartridge is over the print location, oneprimary color dot is printed on the paper when called for by the primarycolor dot data; and means for stopping the print carriage from movingfrom the second side to the first side once both print cartridges are tothe first side of the print location.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a block diagram of a system which converts a full colorimage to a two/three color image according to an embodiment of theinvention.

FIG. 2 shows a method for converting a full color image to a two/threecolor image according to an embodiment of the invention.

FIG. 3 shows a block diagram of a system which prints a two/three colorreceipt on a POS printer using a single pass for each line of printaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a host system 10 contains a color image to beprinted. Host system 10 is typically some type of computing device,preferably a PC or equivalent. The image is contained in the memory ofhost system 10, including color information for the image. “Colorinformation” as used in this application means a color as that term isgenerally known, such as green, red, blue, yellow, orange, etc., butexcluding black and white. The term “color” by itself includes black andwhite.

A driver 20 converts the image from host system 10 into commands that aprinter 30 can understand. Various printer command protocols are knownto those in the art. Driver 20 can be implemented in hardware, software,or a combination of hardware and software, and can be a separate deviceor contained in either host system 10 or printer 30.

Printer 30 converts the color information received from driver 20 into aprinted image that contains a primary color, an alternate color, and abackground color. The primary color and alternate color are provided byink jet pens (cartridges) such as those manufactured and sold byHewlett-Packard, while the background color is provided by the paperstock the image is printed on. The background color is usually whitesince most paper, including that typically used for receipts, is white.The primary color is usually black, but does not have to be black aslong as it is available in ink jet cartridge form. The alternate colorcan be any color available in ink jet cartridge form.

A “color value” is defined as any combination of data that defines theintensity of a color for a dot/pixel. In the plural, “color values”means a combination of one or more color values that makes up all thecolor intensity information for a dot/pixel, since display pixels caninclude varying amounts of red, green, and blue (RGB) or cyan, magenta,and yellow (CMY). If a color value for a particular color exceeds agiven threshold, that color value is ON. If a color value for aparticular color is below a given threshold, that color value is OFF.

The preferred coding for converting a full color image to a 2-colorimage is as follows. If all color values are OFF, the primary color isprinted. If all color values are ON, no printing is done, resulting in adot (space) of the background color. If a color value is ON that is thesame color as the alternate color, a dot of the alternate color isprinted. If the primary color is something other than black, a dot ofthe primary color is printed if a color value is ON that is the samecolor as the primary color. Color values communicated to printer 30 fora particular dot/pixel that do not fit the aforementioned cases areignored, i.e., no color is printed resulting in a dot of the backgroundcolor. This is summarized in Table 1.

TABLE 1 Primary Color Alternate Color Result ON ON Background Color ONOFF Primary Color OFF ON Alternate Color OFF OFF Primary Color

The printer and method of the present invention does adjust the hue orsaturation of the dots. It prints saturated dots of a predefined hue.Graphics images that are generated in a full color RGB or CMYenvironment are converted by the present invention for printing on a2-color printer such as the PJ1000 Spot Color Printer manufactured bythe Ithaca, N.Y. facility of TransAct Technologies, Inc. This is done byreading the full color image into the printer 30 program and convertingit to a true color RGB image. The true color image is then processed toremove hue, saturation and all but 3 colors. The first two colors arepreferably white and black. The third color is selected to match thecolor of the color cartridge in the printer. This conversion process canbe adjusted by adjusting the saturation points where each color isconverted to on or off.

A two-color printer such as the Ithaca POSjet™1000 Printer typically haswhite (the paper), black (an ink cartridge), and one other premixedcolor (for example, red). The printer does not mix the inks on thepaper. It either leaves the paper color, prints a black dot, or a colordot. To allow the printer to use colors other than red, the architectureof the color provides for the sending of three color planes to theprinter.

Because the printer does not mix colors, either CMY or RGB colordefinitions work. RGB color definition is preferable because the colorsare closer to those most often used in print, and as a result, RGB colordefinition generally requires sending less data to the printer. RGBcolor definition also is convenient for use with Microsoft® Windows® togenerate data because it is the same as the display.

When a graphic is created for the 2-color printer, the colors used inthe graphic must take into account the fact that colors other than thesecondary pen color may print black or may not print at all.

There are some special considerations printing images on a 2- colorprinter such as the Ithaca POSjet™ Printer. The driver in printer 30converts colors that the printer cannot print into an image as best itcan. Color in the image that the printer does not have will not beprinted. An example of this is an image that has green in it beingprinted on a printer that has black and red print cartridges. The greencontent in the image is not printed. Conversely, if an image has orangecontent, then it is printed as red on the printer. This red print wouldresult because orange has a red component to it.

Color intensity also has an impact on how graphic images print on theprinter. If a color's intensity is too low, then it is not printed. If acolor's intensity is very high, i.e., dark, it may get printed in black.

Referring to FIG. 2, the method of the invention is shown in abbreviatedform. The color image is provided on the host in step 50. The pixels ofthe image are converted in step 60 to printer commands. The color valuesfor each pixel are determined in step 70. Then in step 80, the colorvalues are compared to a specified threshold and designated as either ONor OFF. In step 91 the primary color is printed if all color values areOFF, in step 92 the primary color is printed if the primary is ON andthe alternate is OFF, in step 93 the alternate color is printed if thealternate is ON and the primary is OFF, and in step 94 no printing isdone if all color values are ON.

Referring to FIG. 3, raw print data from block 20 of FIG. 1 is sent to amicroprocessor 110. Microprocessor 110 converts the data to the correctformat for primary and alternate print cartridges 114, 116. The data aresent to a print head driver circuit 112 which drives print cartridges114, 116, that is, print driver circuit 112 fires dots of ink fromcartridges 114, 116 onto the paper. Path A is the print controlinformation path from microprocessor 110 to print head driver circuit112 to primary and alternate print cartridges 114, 116.

Path B shows the path of carriage stepper motor control signals frommicroprocessor 110 to a carriage motor driver circuit 120 to a carriagemotor 122. Path C shows the path of paper advance stepper motor controlsignals from microprocessor 110 to a paper advance motor driver circuit130 to a paper advance motor 132.

Microprocessor 110 needs to be fast enough to perform the processing ofblock 30 of FIG. 1 while at the same time control the printing process,thus rendering the image processing invisible to a user. A 32-bitmicroprocessor running at 33 MHz is adequate for this task.

Stepper motors are preferably used for carriage motor 122 and paperadvance motor 132 so that microprocessor 110 knows precisely where theprint carriage (not shown) is at all times. Since microprocessor 110also controls the printing process, microprocessor 110 knows where theprinted image is at all times, and thus knows where the print carriageis with respect to the printed image.

The following is an example of sequence steps for a method of singlepass printing with a two-color PIS printer.

1) If the print carriage is in the area where the image is to beprinted, move the carriage to the right of the area where the image isto be printed.

2) If the print carriage is to the left of the area where the image isto be printed, go to Step 11.

3) Both print cartridges are at the right side of the area where theimage is to be printed.

4) Under software control via electronics and mechanics, the printcarriage begins travel to the left.

5) When the primary color cartridge is over the area where the image isto be printed, it prints any primary color dot present in the image tobe printed.

6) When the alternate color cartridge is over the area where the imageis to be printed, it prints any alternate color dot present in the imageto be printed.

7) As carriage travel continues to the left, the primary color andalternate color cartridges print as specified by the image data in thesingle carriage pass.

8) Carriage travel continues to the left until both cartridges are tothe left of the image area being printed.

9) The paper that the image is printed on is advanced an amount equal tothe height of the information printed in this pass of the carriage.

10) If no more image is to be printed, go to step 19.

11) Both print cartridges are at the left side of the area where theimage is to be printed

12) Under software control via electronics and mechanics, the printcarriage begins travel to the right.

13) When the alternate color cartridge is over the area where the imageis to be printed, it prints any alternate color dot present in the imageto be printed.

14) When the primary color cartridge is over the area where the image isto be printed, it prints any primary color dot present in the image tobe printed.

15) Carriage travel continues to the right and the primary color andalternate color cartridges print as specified in the image data in thesingle carriage pass.

16) Carriage travel continues to the right until both cartridges are tothe right of the image being printed.

17) The paper that the image is printed on is advanced an amount equalto the height of the information printed in this pass of the carriage.

18) If there is more of the image to be printed, go to Step 3.

19) Done.

While the present invention has been described with reference to aparticular preferred embodiment and the accompanying drawings, it willbe understood by those skilled in the art that the invention is notlimited to the preferred embodiment and that various modifications andthe like could be made thereto without departing from the scope of theinvention as defined in the following claims.

What is claimed is:
 1. A method of printing a color image using singlepass printing, comprising the steps of: providing a two-color printerfor printing said image on a paper; providing a plurality of printercommands representing data from said image to be printed, said databeing in a form of primary color dot data, alternate color dot data, andno-print dot data; at a beginning of a single pass, determining alocation of a printer carriage with respect to a print location of saidimage being printed on said paper, wherein said printer carriagecontains only two print cartridges, namely, a primary color cartridgeand an alternate color cartridge corresponding to a primary color and analternate color, respectively; at said beginning of said single pass,moving said printer carriage to a second side of said print location ifsaid printer carriage is on a first side of said print location, andwhen said primary color cartridge is over said print location, oneprimary color dot is printed on said paper where called for by saidprimary color dot data; after which, when said alternate color cartridgeis over said print location, one alternate color dot is printed on saidpaper when called for by said alternate color dot data; stopping saidprint carriage from moving from said first side to said second side onceboth print cartridges are to said second side of said print location atan end of said single pass; at said beginning of said single pass,moving said printer carriage to said first side of said print locationif said printer carriage is on said second side of said print location,and when said alternate color cartridge is over said print location, onealternate color dot is printed on said paper where called for by saidalternate color dot data; after which, when said primary color cartridgeis over said print location, one primary color dot is printed on saidpaper when called for by said primary color dot data; and stopping saidprint carriage from moving from said second side to said first side onceboth print cartridges are to said first side of said print location atsaid end of said single pass.
 2. A method according to claim 1, furthercomprising the step of advancing said paper in said printer after saidprint carriage is stopped at said end of said single pass.
 3. A methodaccording to claim 2, wherein said steps of moving alternate with eachother until said image is completely printed.
 4. A method according toclaim 1, further comprising the step of moving said printer carriage tosaid second side of said print location if said printer carriage is oversaid print location.
 5. An apparatus for printing a color image usingsingle pass printing, comprising: a two-color printer for printing saidimage on a paper; means for providing a plurality of printer commandsrepresenting data from said image to be printed, said data being in aform of primary color dot data, alternate color dot data, and no-printdot data; means for determining a location of a printer carriage withrespect to a print location of said image being printed on said paper,wherein said printer carriage contains only two print cartridges,namely, a primary color cartridge and an alternate color cartridgecorresponding to a primary color and an alternate color, respectively;means for moving said printer carriage to a second side of said printlocation if said printer carriage is on a first side of said printlocation at a beginning of a single pass, and when said primary colorcartridge is over said print location, one primary color dot is printedon said paper where called for by said primary color dot data; afterwhich, when said alternate color cartridge is over said print location,one alternate color dot is printed on said paper when called for by saidalternate color dot data; means for stopping said print carriage frommoving from said first side to said second side once both printcartridges are to said second side of said print location at an end ofsaid single pass; means for moving said printer carriage to said firstside of said print location if said printer carriage is on said secondside of said print location at said beginning of said single pass, andwhen said alternate color cartridge is over said print location, onealternate color dot is printed on said paper where called for by saidalternate color dot data; after which, when said primary color cartridgeis over said print location, one primary color dot is printed on saidpaper when called for by said primary color dot data; and means forstopping said print carriage from moving from said second side to saidfirst side once both print cartridges are to said first side of saidprint location at an end of said single pass.
 6. An apparatus accordingto claim 5, further comprising means for advancing said paper in saidprinter after said print carriage is stopped at said end of said singlepass.
 7. An apparatus according to claim 6, further comprising means foralternating lines of printing in each direction until said image iscompletely printed.
 8. An apparatus method according to claim 5, furthercomprising means for moving said printer carriage to said second side ofsaid print location if said printer carriage is over said printlocation.